apache/docs/manual/mod/mod_privileges.xml

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<modulesynopsis metafile="mod_privileges.xml.meta">

<name>mod_privileges</name>
<description>Support for Solaris privileges and for running virtual hosts
under different user IDs.</description>
<status>Experimental</status>
<identifier>privileges_module</identifier>
<compatibility>Available in Apache 2.3 and up, on Solaris 10 and
OpenSolaris platforms</compatibility>

<summary>
<p>This module enables different Virtual Hosts to run with different
Unix&trade; <var>User</var> and <var>Group</var> IDs, and with different
<a href="http://www.sun.com/bigadmin/features/articles/least_privilege.jsp"
>Solaris Privileges</a>.  In particular, it offers a solution to the
problem of privilege separation between different Virtual Hosts, first
promised by the abandoned <module>perchild</module> MPM.
It also offers other security enhancements.</p>

<p>Unlike <module>perchild</module>, <module>mod_privileges</module>
is not itself an MPM.  It works <em>within</em> a processing model to
set privileges and User/Group <em>per request</em> in a running process.
It is therefore not compatible with a threaded MPM, and will refuse
to run under one.</p>

<p><module>mod_privileges</module> raises security issues similar to
those of <a href="../suexec.html">suexec</a>.  But unlike suexec,
it applies not only to CGI programs but to the entire request processing
cycle, including in-process applications and subprocesses.
It is ideally suited to running PHP applications under <strong>mod_php</strong>,
which is also incompatible with threaded MPMs.  It is also well-suited
to other in-process scripting applications such as <strong>mod_perl</strong>,
<strong>mod_python</strong>, and <strong>mod_ruby</strong>, and to
applications implemented in C as apache modules where privilege
separation is an issue.</p>

</summary>

<section id="security"><title>Security Considerations</title>
<p>There are three principal security concerns with mod_privileges:</p>
<ul><li>Running as a system user introduces the same security issues
    as mod_suexec, and near-equivalents such as cgiwrap and suphp.</li>
<li>A privileges-aware malicious user extension (module or script)
    could escalate its privileges to anything available to the
    httpd process in any virtual host.</li>
<li>A privileges-aware malicious user extension (module or script)
    could escalate privileges to set its user ID to another
    system user (and/or group).</li>
</ul>

<p>The first is amply discussed in the suexec page and elsewhere, and
doesn't need repeating here.  The second and third boil down to one
principle: ensure no untrusted privileges-aware code can be loaded.
</p>

<p>There are several ways privileges-aware code could be loaded into Apache:</p>
<ul>
<li>within the base system (e.g. mod_privileges itself if statically linked).</li>
<li>Loaded at startup using a LoadModule or LoadFile directive.</li>
<li>Loaded at startup indirectly by an application module such as mod_php.</li>
<li>Loaded at runtime by an application module or script.</li>
</ul>

<p>What gets loaded at startup is under the control of the sysop, and
relatively easy to deal with.  A tool will be provided to audit your
installation.  That leaves code loaded in the course of processing a
request as the threat.  There is unfortunately no generic way apache
can control what a script running under an application module can load,
so you should use the security provided by your scripting module
and language.</p>

<section><title>Security with mod_php</title>

<p>There is no known PHP extension supporting Solaris privileges, so it
is unlikely that a script could escalate privileges unless it can
load external (non-PHP) privileges-aware code.  However, you should
nevertheless audit your mod_php installation.</p>

<p>To prevent scripts loading privileges-aware code, PHP's dl() function
should be disabled.  This is automatic in safe mode.</p>

</section>

<section><title>Security with mod_perl</title>

<p>Perl has an extension Sun::Solaris::Privileges that exposes the privileges
API to scripts.  You should ensure this extension is NOT installed if you
have untrusted users.</p>

<p>You will also need to ensure that your users cannot load shared objects
(including PerlXS) from their own user directories, or that if this is
enabled, the entire user-space must be carefully audited.</p>
</section>

<section><title>Security with mod_python</title>

<p>There is no known Python extension supporting Solaris privileges, so it
is unlikely that a script could escalate privileges unless it can
load external (non-Python) privileges-aware code.  However, you should
nevertheless audit your mod_ruby installation.</p>

<p>*** What are the issues of Python loading a shared object?</p>
</section>

<section><title>Security with mod_ruby</title>

<p>There is no known Ruby extension supporting Solaris privileges, so it
is unlikely that a script could escalate privileges unless it can
load external (non-Ruby) privileges-aware code.  However, you should
nevertheless audit your mod_ruby installation.</p>

<p>*** What are the issues of Ruby loading a shared object?</p>
</section>

<section><title>Security with Lua/mod_wombat</title>

<p>???</p>
</section>
<section><title>Security with scripts</title>
<p>The security issues of mod_privileges do not affect scripts such as
traditional CGI, which run in a separate process.  That includes
PHP, Perl, Python, Ruby, etc, run out-of-process.</p>
</section>
</section>
<directivesynopsis>
<name>VHostUser</name>
<description>Sets the User ID under which a virtual host runs.</description>
<syntax>VHostUser <var>unix-userid</var></syntax>
<default>Inherits the userid specified in
<directive module="mod_unixd">User</directive></default>
<contextlist><context>virtual host</context></contextlist>
<compatibility>Available on Solaris 10 and OpenSolaris with
non-threaded MPMs (<module>prefork</module> or custom MPM).</compatibility>

<usage>
    <p>The <directive>VHostUser</directive> directive sets the Unix userid
    under which the server will process requests to a virtualhost.
    The userid is set before the request is processed and reset afterwards
    using <a
    href="http://www.sun.com/bigadmin/features/articles/least_privilege.jsp"
    >Solaris Privileges</a>.  Since the setting applies to the
    <em>process</em>, this is not compatible with threaded MPMs.</p>
    <p><var>Unix-userid</var> is one of:</p>
    <dl>
      <dt>A username</dt>
      <dd>Refers to the given user by name.</dd>

      <dt><code>#</code> followed by a user number.</dt>
      <dd>Refers to a user by its number.</dd>
    </dl>

    <note type="warning"><title>Security</title>
    <p>This directive cannot be used to run apache as root!
    Nevertheless, it opens potential security issues similar to
    those discussed in the <a href="../suexec.html">suexec</a>
    documentation.</p></note>
</usage>
<seealso><directive module="mod_unixd">User</directive></seealso>
<seealso><directive module="mod_suexec">SuexecUserGroup</directive></seealso>
</directivesynopsis>

<directivesynopsis>
<name>VHostGroup</name>
<description>Sets the Group ID under which a virtual host runs.</description>
<syntax>VHostGroup <var>unix-groupid</var></syntax>
<default>Inherits the group id specified in
<directive module="mod_unixd">Group</directive></default>
<contextlist><context>virtual host</context></contextlist>
<compatibility>Available on Solaris 10 and OpenSolaris with
non-threaded MPMs (<module>prefork</module> or custom MPM).</compatibility>

<usage>
    <p>The <directive>VHostGroup</directive> directive sets the Unix group
    under which the server will process requests to a virtualhost.
    The group is set before the request is processed and reset afterwards
    using <a
    href="http://www.sun.com/bigadmin/features/articles/least_privilege.jsp"
    >Solaris Privileges</a>.  Since the setting applies to the
    <em>process</em>, this is not compatible with threaded MPMs.</p>
    <p><var>Unix-group</var> is one of:</p>
    <dl>
      <dt>A group name</dt>
      <dd>Refers to the given group by name.</dd>

      <dt><code>#</code> followed by a group number.</dt>
      <dd>Refers to a group by its number.</dd>
    </dl>

    <note type="warning"><title>Security</title>
    <p>This directive cannot be used to run apache as root!
    Nevertheless, it opens potential security issues similar to
    those discussed in the <a href="../suexec.html">suexec</a>
    documentation.</p></note>
</usage>
<seealso><directive module="mod_unixd">Group</directive></seealso>
<seealso><directive module="mod_suexec">SuexecUserGroup</directive></seealso>
</directivesynopsis>

<directivesynopsis>
<name>VHostSecure</name>
<description>Determines whether the server runs with enhanced security
for the virtualhost.</description>
<syntax>VHostSecure On|Off</syntax>
<default>VHostSecure On</default>
<contextlist><context>virtual host</context></contextlist>
<compatibility>Available on Solaris 10 and OpenSolaris with
non-threaded MPMs (<module>prefork</module> or custom MPM).</compatibility>

<usage>
    <p>Determines whether the virtual host processes requests with
    security enhanced by removal of <a
    href="http://www.sun.com/bigadmin/features/articles/least_privilege.jsp"
    >Privileges</a> that are rarely needed in a webserver, but which are
    available by default to a normal Unix user and may therefore
    be required by modules and applications.  It is recommended that
    you retain the default (On) unless it prevents an application running.
    Since the setting applies to the <em>process</em>, this is not
    compatible with threaded MPMs.</p>
    <note><title>Note</title>
    <p>If <directive>VHostSecure</directive> prevents an application
    running, this may be a warning sign that the application should be
    reviewed for security.</p></note>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>VHostCGIMode</name>
<description>Determines whether the virtualhost can run
subprocesses, and the privileges available to subprocesses.</description>
<syntax>VHostCGIMode On|Off|Secure</syntax>
<default>VHostCGIMode On</default>
<contextlist><context>virtual host</context></contextlist>
<compatibility>Available on Solaris 10 and OpenSolaris with
non-threaded MPMs (<module>prefork</module> or custom MPM).</compatibility>

<usage>
    <p>Determines whether the virtual host is allowed to run fork and exec,
    the <a
    href="http://www.sun.com/bigadmin/features/articles/least_privilege.jsp"
    >privileges</a> required to run subprocesses.  If this is set to
    <var>Off</var> the virtualhost is denied the privileges and will not
    be able to run traditional CGI programs or scripts under the traditional
    <module>mod_cgi</module>, nor similar external programs such as those
    created by <module>mod_ext_filter</module> or
    <directive module="mod_rewrite">RewriteMap</directive> <var>prog</var>.
    Note that it does not prevent CGI programs running under alternative
    process and security models such as <a href="http://fastcgi.coremail.cn"
    >mod_fcgid</a>, which is a recommended solution in Solaris.</p>
    <p>If set to <var>On</var> or <var>Secure</var>, the virtual host
    is permitted to run external programs and scripts as above.
    Setting <directive>VHostCGIMode</directive> <var>Secure</var> has
    the effect of denying privileges to the subprocesses, as described
    for <directive>VHostSecure</directive>.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>DTracePrivileges</name>
<description>Determines whether the privileges required by dtrace are enabled.</description>
<syntax>DTracePrivileges On|Off</syntax>
<default>DTracePrivileges Off</default>
<contextlist><context>server config</context></contextlist>
<compatibility>Available on Solaris 10 and OpenSolaris with
non-threaded MPMs (<module>prefork</module> or custom MPM).</compatibility>

<usage>
    <p>This server-wide directive determines whether Apache will run with
    the <a
    href="http://www.sun.com/bigadmin/features/articles/least_privilege.jsp"
    >privileges</a> required to run
    <a href="http://www.sun.com/bigadmin/content/dtrace/">dtrace</a>.
    Note that <var>DTracePrivileges On</var> will not in itself
    activate DTrace, but <var>DTracePrivileges Off</var> will prevent
    it working.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>VHostPrivs</name>
<description>Assign arbitrary privileges to a virtual host.</description>
<syntax>VHostPrivs [+-]?<var>privilege-name</var> [[+-]?privilege-name] ...</syntax>
<default>None</default>
<contextlist><context>virtual host</context></contextlist>
<compatibility>Available on Solaris 10 and OpenSolaris with
non-threaded MPMs (<module>prefork</module> or custom MPM).
and when <module>mod_privileges</module> is compiled with the
<var>BIG_SECURITY_HOLE</var> compile-time option.</compatibility>

<usage>
    <p><directive>VHostPrivs</directive> can be used to assign arbitrary <a
    href="http://www.sun.com/bigadmin/features/articles/least_privilege.jsp"
    >privileges</a> to a virtual host.  Each <var>privilege-name</var>
    is the name of a Solaris privilege, such as <var>file_setid</var>
    or <var>sys_nfs</var>.</p>

    <p>A <var>privilege-name</var> may optionally be prefixed by
    + or -, which will respectively allow or deny a privilege.
    If used with neither + nor -, all privileges otherwise assigned
    to the virtualhost will be denied.  You can use this to override
    any of the default sets and construct your own privilege set.</p>

    <note type="warning"><title>Security</title>
    <p>This directive can open huge security holes in apache, up to
    and including running requests with root-level powers.  Do not
    use it unless you fully understand what you are doing!</p></note>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>VHostCGIPrivs</name>
<description>Assign arbitrary privileges to subprocesses created
by a virtual host.</description>
<syntax>VHostPrivs [+-]?<var>privilege-name</var> [[+-]?privilege-name] ...</syntax>
<default>None</default>
<contextlist><context>virtual host</context></contextlist>
<compatibility>Available on Solaris 10 and OpenSolaris with
non-threaded MPMs (<module>prefork</module> or custom MPM)
and when <module>mod_privileges</module> is compiled with the
<var>BIG_SECURITY_HOLE</var> compile-time option.</compatibility>

<usage>
    <p><directive>VHostCGIPrivs</directive> can be used to assign arbitrary <a
    href="http://www.sun.com/bigadmin/features/articles/least_privilege.jsp"
    >privileges</a> to subprocesses created by a virtual host, as discussed
    under <directive>VHostCGIMode</directive>.  Each <var>privilege-name</var>
    is the name of a Solaris privilege, such as <var>file_setid</var>
    or <var>sys_nfs</var>.</p>

    <p>A <var>privilege-name</var> may optionally be prefixed by
    + or -, which will respectively allow or deny a privilege.
    If used with neither + nor -, all privileges otherwise assigned
    to the virtualhost will be denied.  You can use this to override
    any of the default sets and construct your own privilege set.</p>

    <note type="warning"><title>Security</title>
    <p>This directive can open huge security holes in apache subprocesses,
    up to and including running them with root-level powers.  Do not
    use it unless you fully understand what you are doing!</p></note>
</usage>
</directivesynopsis>



</modulesynopsis>